In theory, international bodies can help developing/poorer countries handle problems that they don't have the infrastructure/knowledge base to address on their own. The WHO historically contributed to efforts to eradicate smallpox, etc. Foreign aid is a pretty small chunk of the US budget, so if the money is actually being used well, it's not a problem and it can help people.

Unfortunately many NGOs are incompetent and/or scams, and UN agencies are the same except with certain agendas instead of scamming.